1. Field of the Invention
The present invention relates to an ink set including plural inks each containing a pigment as a coloring material, an ink jet recording method using the ink set and an ink jet recording apparatus.
2. Description of the Related Art
In late years, a pigment ink containing a pigment as a coloring material is widely applied as an ink for ink jet printing not only to compact printers for office or home use but also to wide format printers used for printing posters and advertisements. A wide variety of recording media is used for the wide format printers, including, for example, glossy paper, mat paper, plain paper and besides, art paper which allows the texture of the base material to be felt.
Examples of the pigment used for the pigment ink include polymer dispersion pigments (see Japanese Patent Application Laid-Open No. H06-306317) dispersed in aqueous media with a dispersion polymer having a hydrophobic moiety and a hydrophilic moiety and self-dispersion pigments (see Japanese Patent Application Laid-Open No. 2002-322394 and Japanese Patent Application Laid-Open No. 2007-099916) formed by introducing hydrophilic groups onto the surface of pigment particles. Images recorded on glossy paper with an ink containing a polymer dispersion pigment are excellent in glossiness. In the meantime, images recorded on plain paper, mat paper, art paper with an ink containing a self-dispersion pigment are high in image density and besides excellent in anti-bleeding properties and character quality. In late years, it has been also proposed to use an ink containing a polymer dispersion pigment and an ink containing a self-dispersion pigment in combination for recording images so as to attain good image quality regardless of the kind of the recording media (see Japanese Patent Application Laid-Open No. 2003-213170).
In addition, considerably large recording media of the size such as A0 size or A1 size are often used in the printing with wide format printers, and when the recording media with images recorded thereon are carried, they are commonly rolled up to a cylindrical form, which may cause the following problems. That is, when a recording medium is rolled up, the images may be scratched with a sharp part such as a corner of the recording medium, and in such a case, there is caused a problem at considerable frequency that the image recorded with a pigment ink is damaged while the coloring material thereof falls off. In addition, when an image recorded with a pigment ink on art paper is stuck as a picture on the wall, the problem that the coloring material falls off is also caused at considerable frequency in a case where the image is strongly scratched with a sharp member such as a nail of a person. As described above, when a pigment ink is selected as an ink used for a wide format printer, it becomes an important problem to be overcome to attain a much higher level of scratch resistance than the conventional pigment ink so as to prevent the coloring material of the image from falling off even when the image is touched with a sharp member.
Meanwhile, because the scratch resistance of the image recorded with a pigment ink has been a problem so far, various methods for solving such a problem have been suggested. However, most of them have been considered as a pigment ink for compact printers used at office and home, what is achieved at best by using related art is to attain scratch resistance of such a degree that the image is not damaged when it is touched with a finger. That is, the problem in scratch resistance as mentioned above which is sufficient to cope with the case where the image is touched with a sharp member has not been still solved.
Needless to say, there have been some suggestions on the methods for attaining a higher level scratch resistance of the images so as to enable to provide images which can satisfy scratch resistance in such a situation that the images may be touched with a sharp member. For example, there is a suggestion for improving the scratch resistance of the images by imparting a specific compound onto the images recorded with an ink for ink jet recording, thereby enhancing slipping properties of the images (see Japanese Patent Application Laid-Open No. 2000-108495 and Japanese Patent Application Laid-Open No. 2004-284362). There is also a suggestion for improving scratch resistance and scratch resistance of the images by using an ink containing a specific polymer and a specific polyether modified organosiloxane (see Japanese Patent Application Laid-Open No. 2003-192964).
The present inventors have performed the following studies in order to provide an ink set formed by independently combining two or more pigment inks which can be applied to a wide format printer. Specifically, the present inventors have conducted studies on pigment inks which enable to record images as unsusceptible as possible when touched with a sharp member such as a nail of a person. The studies have been conducted mainly on the art described in the patent documents mentioned above. It has been found through the studies that slipping properties can be imparted to the images by incorporating a modified siloxane compound in a pigment ink, so as to obtain a pigment ink which enables to record images superior in scratch resistance to the conventional pigment inks. However, it has been also found through the studies that inks containing a self-dispersion pigment cause a new problem to be solved that the scratch resistance of the images is hard to improve when a modified siloxane compound is incorporated as compared to inks containing a polymer dispersion pigment. It has been also found that the problem to be solved mentioned above is more significantly caused particularly when the density of hydrophilic groups, which are introduced to the surface of the pigment particles in order to attain high image density, is reduced.
Further studies by the present inventors have revealed that when images are recorded using an ink set combining an ink containing a self-dispersion pigment and an ink containing a modified siloxane compound together, there is caused a phenomenon that the scratch resistance of the obtained images decreases. That is, when a self-dispersion pigment and a modified siloxane compound mix with each other on a recording medium, there has occurred a phenomenon similar to the phenomenon as mentioned above which occurs in an ink containing a self-dispersion pigment and a modified siloxane compound together. This means that although recording of images with high image density is possible when an ink containing a self-dispersion pigment is used, this effect is not sufficiently obtained when the ink is combined with an ink containing a modified siloxane compound together for the purpose of improving scratch resistance of the recorded images.
Therefore, an object of the present invention is to provide an ink set which enables to obtain images with improved image density and improved scratch resistance together when the images are recorded by combining an ink containing a self-dispersion pigment and an ink containing a modified siloxane compound. Another object of the present invention is to provide an ink jet recording method and an ink jet recording apparatus which achieves image recording having high image density and excellent scratch resistance by using an ink set formed by combining plural inks together.